Methods for the treatment and prophylaxis of HIV and AIDS

ABSTRACT

The present invention is directed to methods for inhibition of HIV reverse transcriptase, treatment of infection by HIV, prophylaxis of infection by HIV, and the treatment, prophylaxis and/or delay in the onset or progression of AIDS or ARC by administering a compound of structural Formula I 
                         
or a pharmaceutically acceptable salt or co-crystal thereof, wherein X is —F or —Cl, less frequently than once daily.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/294576, filed Feb. 12, 2016, and to U.S. Provisional Application No.62/297657, filed Feb. 19, 2016. Each of the aforementioned applicationsto which this application claims priority is herein incorporated byreference in its entirety.

REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY

The sequence listing of the present application is submittedelectronically via EFS-Web as an ASCII formatted sequence listing with afile name “24294-SEQLIST-26JULY2017.txt”, having a creation date of Jul.26, 2017 and a size of 1.65 kb. This sequence listing submitted viaEFS-Web is part of the specification and is herein incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

Human immunodeficiency virus (HIV-1) infection is a serious conditionwhich if left untreated ultimately destroys the host's immune systemresulting in acquired immunodeficiency syndrome (AIDS) and prematuredeath. Despite advances in antiretroviral therapies (ART), HIV continuesto be a global epidemic and a global public health priority. Anestimated 35 million people worldwide were living with HIV in 2012(Global Report: UNAIDS report on the global AIDS epidemic 2013.UNAIDS/JC2502/1/E). In the U.S., an estimated 1.2 million people areliving with HIV and about 50,000 become newly infected each year. HIVseropositive individuals are initially asymptomatic but typicallydevelop AIDS related complex (ARC) followed by AIDS. More than 650,000people in the U.S. have died with AIDS and more than 14,000 additionaldeaths are reported each year. Treatment can help people with HIV livelonger, healthier lives, but currently only 30 percent of people withHIV in the U.S. are successfully keeping their virus under control.(Center for Disease Control and Prevention. Today's HIV/AIDS epidemic.July 2015).

Nucleoside reverse transcriptase inhibitors (NRTIs or NsRTIs) inhibitHIV reverse transcriptase and block HIV replication. They are one of 6classes of HIV antiretrovirals (ARVs) used as components of potent anddurable multi-drug regimens that typically combine two NRTIs (or an NRTIwith an NtRTI) with a non-nucleoside reverse transcriptase inhibitor, anintegrase strand transfer inhibitor, or a protease inhibitor.Combination treatment maximizes treatment response and minimizes theemergence of drug resistance.

Due to the fact that HIV replication is asynchronous, antiretroviralagents need to be continuously present in patients to effectivelysuppress viremia. For most classes of drugs including proteaseinhibitors, integrase inhibitors, and non-nucleoside reversetranscriptase inhibitors, efficacy is dictated by circulating drugconcentrations and dosing is aimed at providing circulating drugconcentrations throughout the dosing interval (i.e. Cmin) that exceedthose required to suppress viral replication (i.e. the IC50 or IC95). Incontrast, upon entering cells, NRTIs and nucleotide reversetranscriptase inhibitors (NtRTIs such as tenofovir) enter into obligateintracellular anabolic pathways for conversion to active phosphorylatedforms, and it is their intracellular half-lives rather than their plasmaconcentrations that dictate their persistent effect. All currentlyapproved NRTIs and NtRTIs are administered at least once-daily.

4′-Ethynyl-2-fluoro-2′-deoxyadenosine (EFdA) is a nucleoside reversetranscriptase inhibitor that blocks HIV-1 and SIV viral replication invitro (Kawamoto, A., Kodama, E., Sarafianos S. F. et al, Int. J.Biochem. Cell Biol.; 40(11):2410-20 [2008]; Ohrui, H., Kohgo, S.,Hayakawa, H. et al, Nucleosides, Nucleotides & Nucleic Acids, 26,1543-1546 [2007]) and in vivo (Hattori, S., Ide, K., Nakata, H. et al.Antimicrobial. Agents and Chemotherapy, 53, 3887-3893 [2009]).

U.S. Pat. No. 7,339,053 describes EFdA (referred to in the '053 patentas 2′-deoxy-4′-C-ethynyl-2-fluoroadenosine) and4′-ethynyl-2-chloro-2′-deoxyadenosine (referred to herein as ECdA;referred to in the '053 patent as2-chloro-2′-deoxy-4′-C-ethynyladenosine). EFdA and ECdA have thefollowing chemical structures:

Both compounds are metabolized in cells to their active triphosphateanabolite which inhibits HIV reverse transcriptase. In contrast toNsRTIs and NtRTI's currently available for the treatment of HIVinfection, which lack a 3′-OH group to block incorporation of incomingnucleotide, EFdA and ECdA retain a 3′-OH group and act as a chainterminator by preventing translocation of the primer:template in thereverse transcriptase (RT) active site and preventing binding ofincoming deoxyribonucleotides triphosphates (dNTPs). In addition, thepucker of the modified ribose ring of EFdA and ECdA are believed tocontribute to inhibition of reverse transcriptase by placing the 3′-OHin a vector, in which phosphotransfer from the incoming nucleotide isinefficient. (Michailidis E, et al., Mechanism of inhibition of HIV-1reverse transcriptase by 4′-ethynyl-2-fluoro-2′-deoxyadenosinetriphosphate, J Biol Chem 284:35681-35691 [2009]; Michailidis E, et al.,4′-Ethynyl-2-fluoro-2′-deoxyadenosine (EFdA) inhibits HIV-1 reversetranscriptase with multiple mechanisms, J Biol Chem 289:24533-24548[2014]).

In in vitro HIV replication assays, EFdA is a potent antiretroviral andexhibits comparable antiviral activity against clinical isolates acrossall subtypes that have been evaluated. It is rapidly anabolized in bothlymphoid derived cell lines and in peripheral blood mononuclear cells tothe active triphosphate in vitro, and the intracellular half-life ofEFdA Triphosphate (EFdA-TP) exceeds 72 hrs. (Stoddart, C. A., Galkina,et al., Oral Administration of the Nucleoside EFdA(4′-Ethynyl-2-Fluoro-2′-Deoxyadenosine) Provides Rapid Suppression ofHIV Viremia in Humanized Mice and Favorable Pharmacokinetic Propertiesin Mice and the Rhesus Macaque, Antimicrob Agents Chemother, 2015 July;59(7): 4190-4198, Published online 2015 May 4).

EFdA has been shown to have efficacy in animal models of HIV infectionincluding humanized mouse models and an SIV infected rhesus macaquemodel. Pharmacokinetic studies of orally administered EFdA in mouse andrhesus monkey have demonstrated rapid absorption and robust conversionof the nucleoside to the active triphosphate in peripheral bloodmononuclear cells (PBMCs). Drug concentrations achieved in bothhumanized mice and rhesus macaques were efficacious in suppressingviremia when administered to HIV and SIV infected animals, respectively.PBMCs that were isolated from uninfected monkeys 24 hr after drugadministration were refractory to SIV infection. (Ibid.) Currentlyavailable drug treatments for HIV infection work in combination tosuppress viremia, keeping the virus under control. HIV drug therapy islife-long and strict adherence to treatment regimens is critical tomaintain viral suppression, reduce the risk of drug resistance, andminimize the risk of transmission. Efficacious and safe, well-tolerateddrugs that are easy to take with low dosing frequency have the potentialto improve a patient's adherence and long-term treatment success. Forprophylaxis against HIV infection, the only currently availablepre-exposure prophylaxis (PrEP) treatment approved by the U.S. Food andDrug Administration is TRUVADA® (emtricitabine/tenofovir DF) forprophylaxis against HIV infection in uninfected people.

Currently available orally administered anti-retroviral drugs are dosedonce-daily. Less frequent dosing may help to alleviate both practicalchallenges and the cumulative psychological impact of taking daily HIVmedications. Long-acting ARTs may potentially help patients return to agreater sense of normalcy and provide flexibility that could impact theway they live, work, travel, relate to others, and see themselves.Additionally, lessons from other chronic diseases requiring life-longtreatment such as osteoporosis and type-2 diabetes have shown that somepatients adapt to and may prefer once-weekly over once-daily dosingregimens which can result in improved medication adherence.

It would be desirable to have additional prophylactic therapy optionsfor people at risk of HIV infection, either by administering a singleactive agent or a combination of active agents. Additionally, it wouldbe desirable to have oral dosing options for HIV therapies, both fortreatment and prophylaxis of HIV infection, that could be administeredless frequently than dosing on a daily basis, to provide furtheralternatives for patients.

SUMMARY OF THE INVENTION

The present invention is directed to pre-exposure prophylaxis (PrEP)treatment using 4′-ethynyl-2-fluoro-2′-deoxyadenosine (EFdA) or4′-ethynyl-2-chloro-2′-deoxyadenosine (ECdA), i.e., use of EFdA or ECdA,or a pharmaceutically acceptable salt or co-crystal of either activeagent, for prophylaxis of HIV infection in a subject not infected withHIV who is at risk for said infection. The prophylactic treatment can bevia any route or method of administration, including but not limited toadministration orally, parenterally or using an implantable compositionor device.

The present invention also encompasses treatment of a subject infectedwith HIV by parenteral administration of EFdA or ECdA, or apharmaceutically acceptable salt or co-crystal of either active agent,employing a once-weekly or a less frequent dosing regimen. It furtherencompasses treatment of a subject infected with HIV by administrationof EFdA or ECdA by use of an implantable composition or device which isimplanted into the subject once-weekly or less frequently to deliver theactive agent during the interval of time from one implant to thesubsequent implant.

The present invention is further directed to oral administration of EFdAor ECdA, or a pharmaceutically acceptable salt or co-crystal of eitheractive agent, to a subject employing oral dosing regimens for HIVtherapy wherein EFdA or ECdA is administered less frequently than oncedaily. For example, EFdA or ECdA can be orally administered in a dosageregimen of twice-weekly dosing, once-weekly dosing, bi-weekly dosing,twice-monthly dosing, or once-monthly dosing for the inhibition of HIVreverse transcriptase, treatment of infection by HIV, prophylaxis ofinfection by HIV, and the prophylaxis, treatment, and/or delay in theonset or progression of AIDS and/or ARC.

DESCRIPTION OF THE FIGURES

FIG. 1 is a graph of viral load changes in SIV-infected monkeys from the“Once-weekly efficacy in an SIV infected rhesus monkey model ofHIV-infection” study described in Example 1.

FIG. 2 is a graph of Mean PBMC Concentration versus Time Profiles forEFdA Triphosphate (TP) Following Administration of Once Weekly OralDoses of EFdA for 3 Weeks to Healthy Fasted Subjects (linear scale)(lower, semi-log plot).

FIG. 3 is a graph of Mean EFdA Plasma Concentration versus Time ProfilesFollowing Administration of Once Weekly Oral Doses of EFdA for 3 Weeksto Healthy Fasted Subjects (linear scale, first 24 hr post-dose) (lower,semi-log plot) (N=6, LOQ=3.41 nM).

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the present invention, referred to herein asEmbodiment A, relates to a method for the prophylaxis of HIV infectioncomprising administering to a subject not infected with HIV an effectiveamount of a compound of structural Formula I

or a pharmaceutically acceptable salt or co-crystal thereof, wherein Xis —F or —Cl. An effective amount of said compound may be administeredto the subject once-daily, twice-weekly, once-weekly, bi-weekly,twice-monthly or once-monthly or at less frequent intervals such asonce-quarterly, twice-yearly or once-yearly for prophylaxis of infectionby HIV. In an aspect of this embodiment, an effective amount of saidcompound may be administered to the subject employing a dosing regimenwherein a compound of Formula I or a pharmaceutically acceptable salt orco-crystal thereof, is administered to the subject less frequently thanonce daily.

For prophylactic use against HIV infection in an uninfected subject, thecompounds of Formula I, or a salt or co-crystal thereof, can beadministered by any means that produces contact of the active agent withthe agent's site of action. They can be administered by conventionalmeans available for use in conjunction with pharmaceuticals, either asindividual prophylactic agents or in a combination of prophylacticagents. They can be administered alone, but typically are administeredwith a pharmaceutical carrier selected on the basis of the chosen routeof administration and standard pharmaceutical practice. The compounds ofFormula I can, for example, be administered orally (e.g., via tablet orcapsule), parenterally (including subcutaneous injections, intravenous,intramuscular or intrasternal injection, or other infusion techniques),or by inhalation spray, in the form of one or more unit dosage(s) of apharmaceutical composition containing, individually or combined, aneffective amount of the compound, and conventional non-toxicpharmaceutically acceptable carriers, adjuvants and vehicles for theprophylaxis of infection by HIV. The compounds of Formula I could alsobe administered parenterally via an implantable drug deliverycomposition or device adapted to provide an effective amount of thecompound over an extended period of time.

Solid preparations suitable for oral administration (e.g., powders,pills, capsules and tablets) can be prepared according to techniquesknown in the art and can employ such solid excipients as starches,sugars, kaolin, lubricants, binders, disintegrating agents and the like.Liquid preparations suitable for oral administration (e.g., suspensions,syrups, elixirs and the like) can be prepared according to techniquesknown in the art and can employ any of the usual media such as water,glycols, oils, alcohols and the like. For oral administration, a soliddosage form is preferred, particularly tablets.

Parenteral compositions of the compounds of Formula I can be preparedaccording to techniques known in the art and typically employ sterilewater as a carrier and optionally other ingredients, such as astabilizers and/or solubility aids. Injectable solutions or injectablesuspensions can be prepared according to methods known in the art, forexample, wherein the carrier comprises a saline solution, a glucosesolution or a solution containing a mixture of saline and glucose.Implantable compositions can also be prepared according to methods knownin the art wherein, for example, the carrier comprises the activechemical ingredient with suitable excipients (e.g., polymers), orutilizing an implantable device for drug delivery.

Further description of methods suitable for use in preparingpharmaceutical compositions with the compounds of Formula I and ofingredients suitable for use in said compositions is provided inRemington's Pharmaceutical Sciences, 18^(th) edition, edited by A. R.Gennaro, Mack Publishing Co., 1990 and in Remington—The Science andPractice of Pharmacy, 22nd Edition, published by Pharmaceutical Pressand Philadelphia College of Pharmacy at University of the Sciences,2012, ISBN 978 0 85711-062-6 and prior editions. Description forparenteral formulations can be found, for example, in Wright, Jeremy C.and Burgess, Diane J. (Eds.) Long Acting Injections and Implants(Advances in Delivery Science series), Springer NewYork-Dordrecht-Heidelberg-London, 2012, Print.

In an aspect of Embodiment A, a compound of Formula I could beadministered for prophylaxis of infection by HIV using any suitabledosing regimen, e.g. but not limited to, administration of the compoundof Formula I once daily, twice-weekly, once-weekly, bi-weekly,twice-monthly, once-monthly, once-quarterly, twice-yearly oronce-yearly. In another aspect, a unit dosage of a compound of Formula Icould be administered twice-weekly, once-weekly, bi-weekly,twice-monthly, once-monthly, once-quarterly, twice-yearly or once-yearlyfor prohylaxis of infection by HIV. In a further aspect of Embodiment A,the compound of Formula I could be administered once-weekly, bi-weekly,twice-monthly, once-monthly, once-quarterly (i.e., once every 3 months),twice-yearly (i.e., once every 6 months) or once-yearly.

In another aspect of Embodiment A wherein parenteral administration ofthe compound of Formula I is employed, in addition to the dosingregimens described above, less frequent dosage regimens could be used,for example but not limited to, once every 18 months or bi-annually(once every two years).

Generally, the dosage amount per administration at each time intervalwill increase as the time interval between each administrationincreases.

Preferable methods or routes of administration may also vary dependingon the time interval between doses in a dosing regimen. For example, aneffective amount of a compound of Formula I for prophylactic use couldbe administered orally at, for example but not limited to, once-daily,twice-weekly, once-weekly, bi-weekly, twice-monthly or once-monthlyintervals. While oral administration of one unit dosage is preferred ateach dosing interval, one or more oral unit dosage(s) may be may beadminstered at each dosing interval as needed to deliver the appropriateamount of active agent.

Alternatively, an effective amount of a compound of Formula I forprophylactic use could be administered parenterally at, for example butnot limited to, once-weekly, bi-weekly, twice-monthly, once-monthly,once-quarterly, twice-yearly, once-yearly or at longer intervals, forexample but not limited to, once every 18 months or bi-annually (onceevery two years). The longer the interval between each administration ofthe active agent, the greater the amount of active agent may be neededat each administration. Therefore, one or more unit dosage(s) may beadminstered at each dosing interval as needed to deliver the appropriateamount of active agent, for example, one or more injections or infusionsof the compound of Formula I, or one or more implant compositions ordevices.

Any dosing regimen for prophylactic use can be a continuous dosingregimen or an intermittent dosing regimen.

For prophylactic treatment, the unit dosage amount of EFdA or ECdA canrange from 0.1 mg to 500 mg; or alternatively 0.1 to 400 mg or greaterfor longer interval dosage regimens. The dosage amount per unit dosagewill vary depending on the time interval between doses in a dosingregimen.

Another embodiment of the present invention, referred to herein asEmbodiment B, relates to methods for the inhibition of HIV reversetranscriptase, treatment or prophylaxis of HIV infection which includesthe treatment or prophylaxis of viremia, and the treatment, prophylaxisand/or delay in the onset or progression of AIDS or ARC in a subject inneed thereof, employing a dosing regimen wherein a compound of Formula Ior a pharmaceutically acceptable salt or co-crystal thereof, is orallyadministered to the subject less frequently than once daily. Generally,the dosage amount per administration at each time interval will increaseas the time interval between each administration increases.

EFdA or ECdA, optionally in the form of a salt or co-crystal, can beadministered orally by any means that produces contact of the activeagent with the agent's site of action. The compound can be orallyadministered by conventional means available for use in conjunction withpharmaceuticals, either as an individual therapeutic agent or in acombination of therapeutic agents. It can be administered alone, buttypically would be administered with a pharmaceutical carrier selectedfor oral administration, containing an effective amount of the compoundand one or more conventional non-toxic pharmaceutically acceptablecarriers, adjuvants and/or vehicles. Solid preparations suitable fororal administration, for example but not limited to, tablets, capsules,powders, pills, can be prepared according to techniques known in the artand can employ such solid excipients as starches, sugars, kaolin,lubricants, binders, disintegrating agents and the like. Liquidpreparations suitable for oral administration (e.g., suspensions,syrups, elixirs and the like) can be prepared according to techniquesknown in the art and can employ any of the usual media such as water,glycols, oils, alcohols and the like. For oral administration, a soliddosage form is preferred, particularly tablets.

In one aspect of Embodiment B is a method for the inhibition of HIVreverse transcriptase, the treatment of HIV infection which includes thetreatment or prophylaxis of HIV viremia, and the treatment, prophylaxisand/or delay in the onset or progression of AIDS or ARC in an HIVinfected subject which comprises orally administering to the subject aneffective amount of EFdA or ECdA as a unit dosage, wherein the dosingregimen has a dosing interval range from about once every 3 days toabout once every 30 days (i.e., once-monthly or once per month).Examples of the dosing regimens that can be used for oral administrationof EFdA or ECdA for this method include twice-weekly dosing, once-weeklydosing, bi-weekly dosing, twice-monthly dosing, and once-monthly dosing.The selected dosing regimen would employ a dosage amount peradministration suitable to provide treatment for HIV infection, AIDS orARC, prophylaxis of AIDS or ARC, and/or delay in the onset orprogression of AIDS or ARC, during the interval of time from eachadministration to the next.

In a further aspect of this embodiment, said dosage regimen is acontinuous dosing regimen. Typically, for treatment of HIV infection orAIDS, treatment or prophylaxis of viremia, and prophylaxis against theonset or progression of AIDS or ARC in subjects infected with HIV, theselected continuous dosing regimen is maintained as long as thetherapeutic effect is required or desired.

For treatment of HIV-infected patients, maintaining suppression ofviremia is a desired objective. To achieve that objective, EFdA or ECdAwould preferably be administered employing a continuous dosage regimenin combination with administration of one or more additional anti-HIVagents for as long as HIV viremia is effectively suppressed withoutviremia recrudescence.

In another aspect of Embodiment B is a method for the prophylaxis of HIVinfection in a subject not infected with HIV which comprises orallyadministering to the subject an effective amount of EFdA or ECdA as aunit dosage, wherein the dosing regimen has a dosing interval range fromabout once every 3 days to about once every 30 days. Examples of thedosing regimens for prophylaxis of HIV infection that can be used fororal administration of EFdA or ECdA include twice-weekly dosing,once-weekly dosing, bi-weekly dosing, twice-monthly dosing, andonce-monthly dosing. In one aspect of this embodiment, said dosageregimen is a continuous dosing regimen. In another aspect of thisembodiment, said dosage regimen is an intermittent dosing regimen.

For prophylaxis against HIV-infection in an uninfected subject, EFdA orECdA can be orally administered using either a continuous dosing regimenor an intermittent dosing regimen using one or more of the dosingregimens described herein (e.g., twice-weekly dosing, once-weeklydosing, bi-weekly dosing, twice-monthly dosing, and once-monthly dosing)as long as necessary or desired to prevent or reduce the risk for thetransmission of HIV. The selected dosing regimen would employ a dosageamount per administration suitable to provide prophylactic effect duringthe interval of time from each administration to the next.

While oral administration of one unit dosage is preferred at each dosinginterval, one or more oral unit dosage(s) may be may be adminstered ateach dosing interval as needed to deliver the appropriate amount ofactive agent.

For intermittent dosing regimens for prophylaxis against HIV-infectionin an uninfected subject, a single period of adhering to a dosageregimen (e.g., one dose in one week for a weekly dosing regimen) orconsecutive repeated periods of adhering to a dosage regimen (e.g., onedose per week for 3 consecutive weeks employing a weekly dosing regimen)could be followed by a period of not dosing, followed by another periodof employing a dosing regimen. An example of an intermittent dosingregimen for prophylaxis of HIV infection includes but is not limited to,administering an effective dosage amount of EFdA or ECdA once per weekfor 1 or 2 weeks, then not dosing for 1 or 2 months, then re-startingadministering once-weekly dosing of EFdA or ECdA for 1 or 2 weeks. Theoverall period of time that a subject may use an intermittent dosingregimen can range, for example, from about 1 week to the remaininglifespan of the patient, wherein a dosing regimen, during the period(s)of time it is employed, is less frequent than once daily dosing asdescribed herein.

For oral (e.g., tablets or capsules) administration, the dosage unitsmay each contain from 0.1 mg to 500 mg; or alternatively 0.1 to 400 mgof EFdA or ECdA. The dosage amount per unit dosage will vary dependingon the time interval between doses in a dosing regimen, Examples of unitdosage amounts of EFDA or a pharmaceutically acceptable salt orco-crystal thereof include but are not limited to the following.

For a twice-weekly dosing regimen: each unit dosage may be comprised ofEFdA or ECdA in an amount from 0.5 mg to 25 mg, alternatively from 0.5mg to 10 mg; or more specifically 0.5 mg, 1 mg, 2 mg, 3 mg, 4 mg or 5mg.

For a once-weekly dosing regimen: each unit dosage may be comprised ofEFdA or ECdA in an amount from 1 mg to 50 mg, alternatively from 1 mg to20 mg; or more specifically 1 mg, 2 mg, 3 mg, 4 mg, 5 mg, 6 mg, 7 mg, 8mg, 9 mg or 10 mg.

For a bi-weekly or twice-monthly dosing regimen: each unit dosage may becomprised of EFdA or ECdA in an amount from 2 mg to 100 mg,alternatively from 2 mg to 40 mg; or more specifically 2 mg, 3 mg, 4 mg,5 mg, 6 mg, 7 mg, 8 mg, 9 mg, 10 mg, 11 mg, 12 mg, 13 mg, 14 mg, 15 mg,16 mg, 17 mg, 18 mg, 19 mg or 20 mg.

For a once-monthly dosing regimen: each unit dosage may be comprised ofEFdA or ECdA in an amount from 4 mg to 200 mg, alternatively from 4 mgto 80 mg; or more specifically 4 mg, 5 mg, 6 mg, 7 mg, 8 mg, 9 mg, 10mg, 11 mg, 12 mg, 13 mg, 14 mg, 15 mg, 16 mg, 17 mg, 18 mg, 19 mg or 20mg; 21 mg, 22 mg, 23 mg, 24 mg, 25 mg, 26 mg, 27 mg, 28 mg, 29 mg or 30mg, 31 mg, 32 mg, 33 mg, 34 mg, 35 mg, 36 mg, 37 mg, 38 mg, 39 mg or 40mg.

Dosage amounts for ECdA can be about 2 to 4 times higher than for EFdA.

When EFdA or ECdA is administered as a salt or a co-crystal, referenceto an amount of the compound in milligrams or grams is based on theweight of the free form of EFdA or ECdA (i.e., the non-salt ornon-co-crystal form) of the compound.

The minimum dosage amount of EFdA or ECdA will vary with the dosingregimen, and whether the intended use is for treatment and/orprophylaxis for subjects infected with HIV, or for prophylaxis forsubjects not infected with HIV. A non-limiting example for once-weeklyoral dosing for a subject infected with HIV is a unit dosage comprisingabout 10 mg of EFdA or ECdA for treatment and/or prophylaxis ofconditions as described above. A non-limiting example for once-weeklyoral dosing for prevention of HIV-infection in an uninfected subject isa unit dosage comprising about 2 mg of EFdA or ECdA.

Another embodiment of the present invention, referred to herein asEmbodiment C, relates to methods for the inhibition of HIV reversetranscriptase, treatment of HIV infection which includes the treatmentof viremia, and the treatment, prophylaxis and/or delay in the onset orprogression of AIDS or ARC, by parenterally administering an effectiveamount of a compound of Formula I, or a pharmaceutically acceptable saltor co-crystal thereof, to a subject infected with HIV, employing adosing regimen wherein the compound is parenterally administered lessfrequently than once daily.

The compounds of Formula I can be administered parenterally, includingsubcutaneous injections, intravenous, intramuscular or intrasternalinjection, or other infusion techniques (one or more injections orinfusions may be administered at each dosing interval as needed todeliver the appropriate amount of active agent), or by inhalation spray,in the form of a unit dosage of a pharmaceutical composition containingan effective amount of the compound and conventional non-toxicpharmaceutically acceptable carriers, adjuvants and vehicles for thetreatment of a subject infected with HIV. The compounds of Formula Icould also be administered parenterally via an implantable drug deliverycomposition or device adapted to provide an effective amount of thecompound over an extended period of time. Preparation of parenteralcompositions as described above for use in a subject not infected withHIV (see Embodiment A) are likewise suitable for preparation ofparenteral compositions for treatment of a subject infected with HIV. Acontinuous dosing regimen should be used for treatment of HIV infectedsubjects.

In an aspect of Embodiment C, a unit dosage of an effective amount of acompound of Formula I could be administered parenterally at, for examplebut not limited to, once-weekly, bi-weekly, twice-monthly, once-monthly,once-quarterly, twice-yearly or once-yearly intervals or at longerintervals, for example but not limited to, once every 18 months orbi-annually (once every two years).

In a further aspect of Embodiment C, the compound could be administeredparenterally at once-monthly, once-quarterly, twice-yearly oronce-yearly intervals.

The longer the interval between each administration of the active agent,the greater the amount of active agent may be needed at eachadministration. Therefore, one or more unit dosage(s) may be adminsteredat each dosing interval as needed to deliver the appropriate amount ofactive agent, for example, one or more injections or infusions or one ormore implant compositions or devices comprising a compound of Formula I.

The present invention, which includes all embodiments, aspects, anddescriptions recited herein, is also directed to use of EFdA or ECdA inthe dosing regimens as described above with administration of one ormore anti-HIV agents. An “anti-HIV agent” is any agent which is directlyor indirectly effective in the inhibition of HIV, the treatment orprophylaxis of HIV infection, and/or the treatment, prophylaxis or delayin the onset or progression of AIDS or ARC. It is understood that ananti-HIV agent is effective in treating, preventing, or delaying theonset or progression of HIV infection or AIDS and/or diseases orconditions arising therefrom or associated therewith. For example, thecompounds of Formula I may be effectively administered, whether atperiods of pre-exposure and/or post-exposure, in combination witheffective amounts of one or more other anti-HIV agents selected from HIVantiviral agents, immunomodulators, antiinfectives, or vaccines usefulfor treating HIV infection or AIDS.

The present invention encompasses pharmaceutical compositions comprisingan effective amount of EFdA or ECdA and a pharmaceutically acceptablecarrier. Said composition may comprise EFdA or ECdA as the only activeingredient or may include one or more additional active ingredients.Accordingly, the present invention further encompasses pharmaceuticalcompositions comprising an effective amount of EFdA or ECdA and apharmaceutically acceptable carrier further comprising an effectiveamount of one or more additional anti-HIV agents selected from one ormore of HIV antiviral agents, immunomodulators, and ant-infectiveagents. Within this embodiment, the anti-HIV agent is an antiviralselected from one or more of HIV protease inhibitors, HIV reversetranscriptase inhibitors, HIV integrase inhibitors, HIV fusioninhibitors, HIV entry inhibitors, and HIV maturation inhibitors.

Suitable HIV antivirals for use in combination with a compound of thepresent invention include but are not limited to, for example, thoselisted in Table A.

TABLE A Antiviral Agents for Treating HIV infection or AIDS Name Typeabacavir, ABC, Ziagen ® nRTI abacavir + lamivudine, Epzicom ® nRTIabacavir + lamivudine + zidovudine, Trizivir ® nRTI amprenavir,Agenerase ® PI atazanavir, Reyataz ® PI AZT, zidovudine, azidothymidine,Retrovir ® nRTI capravirine nnRTI darunavir, Prezista ® PI ddC,zalcitabine, dideoxycytidine, Hivid ® nRTI ddI, didanosine,dideoxyinosine, Videx ® nRTI ddI (enteric coated), Videx EC ® nRTIdelavirdine, DLV, Rescriptor ® nnRTI dolutegravir, Tivicay ® InIdoravirine, MK-1439 nnRTI efavirenz, EFV, Sustiva ® , Stocrin ® nnRTIefavirenz + emtricitabine + tenofovir DF, Atripla ® nnRTI + nRTIelvitegravir InI emtricitabine, FTC, Emtriva ® nRTI emtricitabine +tenofovir DF, Truvada ® nRTI emvirine, Coactinon ® nnRTI enfuvirtide,Fuzeon ® FI enteric coated didanosine, Videx EC ® nRTI etravirine,TMC-125 nnRTI fosamprenavir calcium, Lexiva ® PI indinavir, Crixivan ®PI lamivudine, 3TC, Epivir ® nRTI lamivudine + zidovudine, Combivir ®nRTI lopinavir PI lopinavir + ritonavir, Kaletra ® PI maraviroc,Selzentry ® EI nelfinavir, Viracept ® PI nevirapine, NVP, Viramune ®nnRTI PPL-100 (also known as PL-462) (Ambrilia) PI raltegravir, MK-0518,Isentress ™ InI rilpivirine nnRTI ritonavir, Norvir ® PI saquinavir,Invirase ®, Fortovase ® PI stavudine, d4T, didehydrodeoxythymidine,Zerit ® nRTI tenofovir DF (DF = disoproxil fumarate), TDF, Viread ® nRTItenofovir alafenamide fumarate, TAF nRTI tipranavir, Aptivus ® PIvicriviroc EI EI = entry inhibitor; FI = fusion inhibitor; InI =integrase inhibitor; PI = protease inhibitor; nRTI = nucleoside reversetranscriptase inhibitor; nnRTI = non-nucleoside reverse transcriptaseinhibitor. Some of the drugs listed in Table A are used in a salt form;e.g., abacavir sulfate, delavirdine mesylate, indinavir sulfate,atazanavir sulfate, nelfinavir mesylate, saquinavir mesylate.

It is understood that the scope of combinations of the compounds ofFormula I with anti-HIV agents is not limited to the HIV antiviralslisted in Table A, but includes in principle any combination with anypharmaceutical composition useful for the treatment and/or prophylaxisof HIV and AIDS. The HIV antiviral agents and other agents willtypically be employed in these combinations in their conventional dosageranges and regimens as reported in the art, including, for example, thedosages described in the Physicians' Desk Reference, Thomson PDR,Thomson PDR, 57th edition (2003), the 58th edition (2004), or the 59thedition (2005) and the Physicians' Desk Reference (68th ed.). (2014),Montvale, N.J.: PDR Network. The dosage ranges for a compound of thepresent invention in these combinations can be the same as those setforth above.

The present invention also encompasses EFdA or ECdA for use in thepreparation of a medicament useful for any one or more of the inhibitionof HIV reverse transcriptase, the treatment of infection by HIV, theprophylaxis of infection by HIV, or the treatment, prophylaxis and/ordelay in the onset or progression of AIDS or ARC in a subject in needthereof. It further encompasses the administration of EFdA or ECdA incombination with one or more additional anti-HIV agents selected fromone or more of HIV antiviral agents, immunomodulators, andanti-infective agents for use in the preparation of a medicament for anyone or more of the inhibition of HIV reverse transcriptase, thetreatment of infection by HIV, the prophylaxis of infection by HIV, thetreatment of AIDS, or the prophylaxis or delay in the onset orprogression of AIDS in a subject in need thereof. Within this embodimentof the present invention, the anti-HIV agent is an antiviral selectedfrom one or more of HIV protease inhibitors, HIV reverse transcriptaseinhibitors, HIV integrase inhibitors, HIV fusion inhibitors, HIV entryinhibitors, and HIV maturation inhibitors.

An additional embodiment of the present invention includes the methods,pharmaceutical compositions, medicaments, uses and combinations setforth herein, wherein the HIV of interest is HIV-1. Thus, for example,in any of the methods, pharmaceutical compositions, medicaments, usesand combinations using the described dosage regimens set forth herein,EFdA or ECdA is employed in an amount effective against HIV-1; and whenused in combination with one or more anti-HIV agent(s), each additionalanti-HIV agent is an HIV-1 antiviral selected from one or more of HIV-1protease inhibitors, HIV-1 reverse transcriptase inhibitors, HIV-1integrase inhibitors, HIV-1 fusion inhibitors, HIV-1 entry inhibitors orHIV-1 maturation inhibitors.

EFdA and/or ECdA may also exhibit activity against HIV-2 whenadministered twice-weekly, once weekly or less frequently in the dosageregimens described herein. EFdA or ECdA also may exhibit activityagainst drug resistant forms of HIV (e.g. NRTI-associated mutant strainsM184V, M184I, K65R).

The specific dose level and frequency of dosage for any particularpatient may be varied and will depend upon a variety of factorsincluding the activity of the specific compound employed, the metabolicstability and length of action of that compound, the age, body weight,general health, sex, diet, mode and time of administration, rate ofexcretion, drug combination, the severity of the particular condition,and the subject undergoing therapy. In some cases, depending on thepotency of the compound or the individual response, it may be necessaryto deviate upwards or downwards from the given dose. The amount andfrequency of administration may be regulated according to the judgmentof the attending clinician considering such factors.

In another embodiment of the present invention, in each of the methods,pharmaceutical compositions, medicaments, uses, combinations, aspectsand other embodiments described and/or claimed herein, the compound ofFormula I is EFdA or a pharmaceutically acceptable salt or co-crystalthereof (i.e., wherein X is —F).

In another embodiment of the present invention, in each of the methods,pharmaceutical compositions, medicaments, uses, combinations, aspectsand other embodiments described and/or claimed herein, the compound ofFormula I is ECdA or a pharmaceutically acceptable salt or co-crystalthereof (i.e., wherein X is —Cl).

For brevity, the phrase “or a pharmaceutically acceptable salt orco-crystal thereof” is not always recited following the term “compoundof Formula I,” “EFdA” or “ECdA” herein. However, reference to the use ofa compound of Formula I, EFdA or ECdA in the methods, pharmaceuticalcompositions, medicaments, uses, combinations, aspects and otherembodiments described and/or claimed herein is intended include the useof a compound of Formula I, EFdA or ECdA (where each term appears) or apharmaceutically acceptable salt or co-crystal thereof.

The term “subject” or “patient” as used herein refers to an animal,preferably a mammal, most preferably a human, who has been or will bethe object of treatment including prophylactic treatment, observation orexperiment. Human subjects or patients include (1) those infected withHIV with or without AIDS who are seeking treatment for HIV infection,ARC or AIDS, and/or prophylaxis and/or delay in the onset or progressionof ARC or AIDS, and (2) those not infected with HIV who are seeking orreceiving prophylactic treatment to prevent or reduce the risk fortransmission of HIV. In an embodiment of this invention, each of themethods, pharmaceutical compositions, medicaments, uses, combinations,aspects and other embodiments described and/or claimed herein, thesubject is a human subject.

The term “effective amount” as used herein means an amount of a compoundsufficient to inhibit HIV reverse transcriptase, inhibit HIVreplication, exert a prophylactic effect, and/or a exert a therapeuticeffect after administration. One embodiment of “effective amount” is a“therapeutically effective amount” which is an amount of a compound thatis effective for inhibiting HIV reverse transcriptase, inhibiting HIVreplication (either of the foregoing which may also be referred toherein as an “inhibition effective amount”), treating HIV infection,treating AIDS or ARC, and/or slowing progression of AIDS or ARC in apatient. Another embodiment of “effective amount” is a “prophylacticallyeffective amount” which is an amount of the compound that is effectivefor prophylaxis of HIV infection, delaying the onset of AIDS or ARC, orprophylaxis of AIDS or ARC in a patient. It is understood that in an HIVinfected subject, an effective amount could simultaneously be both atherapeutically effective amount, e.g., for treatment of HIV infection,and a prophylactically effective amount, e.g., for prevention orreduction of risk for developing AIDS or ARC or for delaying the onsetor progression of AIDS or ARC.

Prophylaxis (or prevention) of infection by HIV in an uninfected subjectis intended to mean preventing or reducing the likelihood of HIVinfection in the subject. In a subject infected with HIV, prophylaxis(or prevention) of AIDS or ARC is intended to mean preventing orreducing the likelihood for developing AIDS or ARC in the subject.

Another embodiment of “effective amount” encompasses an amount of EFdAor ECdA that reduces viremia in HIV infected subjects or that preventsHIV infection of uninfected people that are exposed to the virus.

In the combination therapies of the present invention, an effectiveamount can refer to each individual agent or to the combination as awhole, wherein the amounts of all agents administered in the combinationare together effective, but wherein a component agent of the combinationmay or may not be present individually in an effective amount withreference to what is considered effective for that component agent if itwere administered alone. The term “administration” and variants thereof(e.g., “administering” a compound) with reference to the methods herein,means providing the compound to the subject in need of treatment orprophylaxis and includes both self-administration and administration tothe patient by another person. When EFdA or ECdA is provided incombination with one or more other active agents (e.g., antiviral agentsuseful for treating or prophylaxis of HIV infection or AIDS),“administration” and its variants are each understood to includeprovision of EFdA or ECdA and the other agent(s) to the subject at thesame time (i.e., all on the same dosing regimen schedule) or atdifferent times if the other agent(s) cannot be dosed on the same dosageregimen schedule as EFdA or ECdA. When the agents of a combination areadministered at the same time, they can be administered together in asingle composition or they can be administered separately.

SIV=Simian Immunodeficiency Virus; VL=viral load; LLQ=lower limit ofquantitation.

Dosing regimens of the present invention that employ dosing of EFdA orECdA less frequently than once daily are described above. Reference todosing “intervals” may also be recited herein to describe dosingregimens. The term “continuous dosing regimen” as used herein, means adosing regimen that is repeated without breaks for as long as thedesired therapeutic effect or prophylactic effect is required or deemedappropriate by a clinician or patient. The term “intermittent dosingregimen” as used herein means a dosing regimen to be used for one ormore limited periods of time for periodic prophylaxis to prevent orreduce the risk for transmission of HIV with stoppage of the dosingregimen after one period or between periods of employing the dosingregimen.

The present invention provides dosing regimens whereby a unit dosage ofthe EFdA or ECdA is regularly administered according to a dosinginterval selected from once-weekly dosing, twice-weekly dosing,bi-weekly dosing, twice-monthly dosing, and once-monthly dosing. Thephrase “once-weekly” dosing as used herein means that a unit dosage ofEFdA or ECdA is administered once per week, i.e. one time during a sevenday period, preferably on the same day of each week. In the once-weeklydosing regimen, the dosage is generally administered about every sevendays. A nonlimiting example of a once-weekly dosing regimen would entailthe administration of a unit dosage of EFdA or ECdA every Sunday. It ispreferred that the unit dosage is administered once every 7 days, butthe once-weekly dosing regimen encompasses a dosing regimen in which aunit dosage is administered every 5 to 10 days as long as twoconsecutive doses fall within two different weekly periods.

The phrase “twice-weekly” dosing as used herein means that a unit dosageof EFdA or ECdA is administered twice per week, i.e., two times during aseven day period, on two different days each weekly period wherein the 2days are preferably the same each week. In the twice-weekly dosingregimen, each unit dosage is generally administered about every three tofour days. A nonlimiting example of a twice weekly regimen would entailthe administration of a unit dosage of EFdA or ECdA every Sunday andWednesday. It is preferred that the unit dosages are administered every3 to 4 days, but the twice weekly dosing regimen encompasses a dosingregimen in which a unit dosage is administered every 2 to 5 days as longas two doses are administered within each weekly period.

The phrase “bi-weekly” dosing as used herein means that a unit dosage ofEFdA or ECdA is administered once during a two week period, i.e. onetime during a fourteen day period, preferably on the same day duringeach two week period. In the bi-weekly dosing regimen, each unit dosageis generally administered once every fourteen days. A non-limitingexample of a bi-weekly dosing regimen would entail the administration ofa unit dosage of EFdA or ECdA every other Sunday. It is preferred thatthe unit dosage is administered once every 14 days, but the bi-weeklydosing regimen encompasses a dosing regimen in which a unit dosage isadministered every 12 to 16 days as long as two consecutive doses fallwithin two different bi-weekly periods.

The phrase “twice-monthly” dosing as used herein means that a unitdosage of EFdA or ECdA is administered twice, i.e. two times, during amonthly calendar period. With the twice-monthly regimen, the doses arepreferably given on the same two dates of each month. In thetwice-monthly dosing regimen, each unit dosage is generally administeredabout every fourteen to sixteen days. A nonlimiting example of atwice-monthly dosing regimen would entail dosing on or about the firstof the month and on or about the fifteenth of the month, i.e. the midwaypoint of the month. It is preferred that the unit dosages areadministered every 14 to 16 days, but the twice-monthly dosing regimenencompasses a dosing regimen in which a unit dosage is administeredevery 13 to 18 days as long as two doses are administered within amonthly period. The twice-monthly regimen is defined herein as beingdistinct from, and not encompassing, the bi-weekly dosing regimenbecause the two regimens have a different periodicity and result in theadministration of different numbers of dosages over long periods oftime. For example, over a one year period, a total of about twenty fourdosages would be administered according to the twice monthly regimen(because there are twelve calendar months in a year), whereas a total ofabout twenty six dosages would be administered according to thebi-weekly dosing regimen (because there are about fifty-two weeks in ayear).

The phrase “once-monthly” (or “once per month”) dosing as used hereinmeans that a unit dosage of EFdA or ECdA is administered once during aone month period, i.e. one time during a monthly calendar period,preferably on the same day during each one month period. In theonce-monthly dosing regimen, each unit dosage is generally administeredonce every 28-31 days. A non-limiting example of a once-monthly dosingregimen would entail the administration of a unit dosage of EFdA or ECdAon or about the first day of every month. It is preferred that the unitdosage is administered once every 28-31 days, but the once-monthlydosing regimen encompasses a dosing regimen in which a unit dosage isadministered every 27 to 33 days as long as two consecutive doses fallwithin two different monthly periods.

The phrase “once-quarterly” dosing as used herein means that a unitdosage of EFdA or ECdA is administered once during a 3 month period,i.e. one time during a quarterly calendar period, preferably on the samedate during each quarterly period. In the once-quarterly dosing regimen,each unit dosage is generally administered once every 84-93 days. Anon-limiting example of this dosing regimen would entail theadministration of a unit dosage of EFdA or ECdA on or about the 1st dayof the first month of each quarterly period. It is preferred that theunit dosage is administered once every 84-93 days, but theonce-quarterly dosing regimen encompasses a dosing regimen in which aunit dosage is administered every 81 to 99 days as long as twoconsecutive doses fall within two different 3 month periods.

The phrase “twice-yearly” dosing as used herein means that a unit dosageof EFdA or ECdA is administered once during a 6 month period, i.e. onetime during a 6 month calendar period, preferably on the same dateduring each twice-yearly period. In the twice-yearly dosing regimen,each unit dosage is generally administered once every 168-186 days. Anon-limiting example of this dosing regimen would entail theadministration of a unit dosage of EFdA or ECdA on or about the 1st dayof the first month of each twice-yearly period. It is preferred that theunit dosage is administered once every 168-186 days, but thetwice-yearly dosing regimen encompasses a dosing regimen in which a unitdosage is administered every 162-198 days as long as two consecutivedoses fall within two different 6 month periods.

The phrase “once-yearly” dosing as used herein means that a unit dosageof EFdA or ECdA is administered once during a 12 month period, i.e. onetime during a 12 month calendar period, preferably on the same dateduring each once-yearly period. In the once-yearly dosing regimen, eachunit dosage is generally administered once every 336-372 days. Anon-limiting example of this dosing regimen would entail theadministration of a unit dosage of EFdA or ECdA on or about the 1st dayof the first month of each once-yearly period. It is preferred that theunit dosage is administered once every 336-372 days, but the once-yearlydosing regimen encompasses a dosing regimen in which a unit dosage isadministered every 324-396 days as long as two consecutive doses fallwithin two different 12 month periods.

EFdA or ECdA can be administered in the form of a pharmaceuticallyacceptable salt or pharmaceutically acceptable co-crystal. The term“pharmaceutically acceptable salt” and “pharmaceutically acceptableco-crystal” refers to a salt or co-crystal which is not biologically orotherwise undesirable (e.g., is neither toxic nor otherwise deleteriousto the recipient thereof). Since EFdA or ECdA contains at least onebasic group on the fluoroadenine base, the present invention includesthe corresponding pharmaceutically acceptable salts. Since EFdA or ECdAcontains at least one basic group on the adenine base, i.e. a groupwhich can be protonated, it can be used according to the presentinvention in the form of its acid addition salts with inorganic ororganic acids such as, for example but not limited to, salts withhydrogen chloride, hydrogen bromide, phosphoric acid, sulfuric acid,nitric acid, benzenesulfonic acid, methanesulfonic acid,p-toluenesulfonic acid, naphthalenedisulfonic acids, trifluoroaceticacid, tartaric acid, lactic acid, salicylic acid, benzoic acid, formicacid, propionic acid, pivalic acid, succinic acid, etc. EFdA or ECdA canbe used according to the present invention in the form of its acidco-crystals with inorganic or organic acids as, for example but notlimited to, salts benzenesulfonic acid, methanesulfonic acid,p-toluenesulfonic acid, naphthalenedisulfonic acids, trifluoroaceticacid, tartaric acid, lactic acid, salicylic acid, benzoic acid, formicacid, propionic acid, pivalic acid, succinic acid, etc. Salts andco-crystals can be obtained from EFdA or ECdA by customary methods whichare known to the person skilled in the art, for example by combinationwith an organic or inorganic acid or base in a solvent or dispersant, orby ion exchange from other salts.

As used herein, the term “composition” is intended to encompass aproduct comprising the specified ingredients, as well as any productwhich results from combining the specified ingredients. Ingredientssuitable for inclusion in a pharmaceutical composition arepharmaceutically acceptable ingredients, which means the ingredientsmust be compatible with each other and not deleterious to the recipientthereof.

EXAMPLE 1

Once-weekly efficacy in an SIV infected rhesus monkey model ofHIV-infection.

Oral efficacy studies were conducted at New Iberia Research Center(NIRC), Lafayette, La. Following treatment with BAYTRIL® (5 mg/kg, IM,SID) for 5 days, 20 monkeys were inoculated intravenously withSIVmac251. After 3 days, venous blood was collected every 2-5 days (2×per week) for viral load testing and monitored to stable viremia(wherein 3 consecutive samples were within 3-fold of each otherfollowing acute viremia peak). Plasma SIV viral RNA levels weredetermined using a branched DNA technique at Siemens Diagnostics,Berkeley, Calif.

Following determination of stable viremia, SIV-infected monkeys wererandomized by age, weight, and viral load (n=3 per group). A 2-armadaptive design was employed in which results from Arm 1 informed thedoses for Arm 2. In Arm 1, animals received two once-weekly doses ofvehicle, 1.3 mg/kg EFdA, or 13 mg/kg EFdA administered via oral gavage.In Arm 2, animals received 3.9 mg/kg or 18.2 mg/kg EFdA once-weekly or0.19 mg/kg EFdA once daily for two weeks. Blood (4 ml) was drawn forviral load determinations during the treatment period on days −2, 0(dosing day), 1, 2, 3, 5, 7 (dosing day), 8, 9, 10, 12, and 14, and thentwo times per week for 3 weeks during the washout period. In addition,blood (1 ml) was drawn on days 0 (2 hrs post dose), 1 (24 hr post dose),7 (2 hrs post dose), and 8 (24 hrs post dose) for EFdA pharmacokineticassessment.

SIV RNA for genotyping was isolated from 140 μl plasma using the QlAampViral RNA Mini kit (Cat# 52904/52906). The reverse transcriptase regionof SIVmac251 was reverse transcribed and amplified using SuperScript IIIRT/Platinum polymerase, primers S251RTF1 (GGCAAAAGGATTAAAGGGAC[2732-2751]) (SEQ ID NO:1) and S251RTR1 (TTTTACTTTGTCTTTGCCCC[4206-4225]) (SEQ ID NO: 2) and 8 μl template RNA in 20 μl reactions. Anested PCR reaction was carried out using 3.5 μl of the product from thefirst reaction with TaKaRa LA Taq and primers S251RTF2(ACAATCATGACAGGGGACAC [2750-2769]) (SEQ ID NO: 3) and S251RTR2(GCTTTCCCTTCTTTTGACTG [4169-4188]) (SEQ ID NO: 4) in 50 μl reactions.After verifying size of ˜1.5 kb by gel electrophoresis, PCR productswere purified using ExoSAP-IT (Affymetrix; cat #78201) and adjusted to15 ng/ml. PCR products (10μl) were mixed with 5 μl 5 μM sequencingprimers S251RTS5 (CAGGGGACACTCCGATTAAC [2760-2779]) (SEQ ID NO: 5),s251RTS6 (AAGGTTCTGCCTCAGGGATG [3266-3285]) (SEQ ID NO: 6), or S251RTS7(CTCAGTCAGGAACAAGAAGG [3755-3774]) (SEQ ID NO: 7). DNA sequencing wascarried out at Genewiz (115 Corporate Blvd, South Plainfield, NJ 07080).

The monkeys showed a high degree of variability in response amongindividuals. Those with high VLs exceeding 10 did not respond as well asthose with low VLs and this contributed to a large standard deviation(FIG. 1). However, the groups were balanced with respect to VL and theaveraged data shows a dose response curve with respect to VL reductionand return of VL upon cessation of dosing (washout). From 3.9 to 18.2mg/kg QW, the VL drop appeared to be close to maximal and, even at 3.9mg/kg, the VL suppression was maintained for 7 days from Day 7 to Day14. One monkey in the vehicle group was euthanized around Day 19 due topoor clinical symptoms. There was a dose-dependent VL rebound during thewash-out period.

These experiments demonstrate that EFdA can control viremia withonce-weekly oral administration as well as once-daily treatment.

EXAMPLE 2

Pharmacokinetics of EFdA following administration of oral doses inhealthy humans.

The pharmacokinetics of EFdA were evaluated in Phase I single andmultiple rising dose studies. In the single dose study, single oraldoses of the oral suspension of EFdA from 5 to 400 mg were administeredto three alternating panels of 8 healthy adult subjects. Within eachpanel, subjects were administered single doses of EFdA (n=6) or matchingplacebo (n=2) in a blinded fashion in up to 3 treatment periods. Panel Areceived 15 mg and 200 mg. Panel B received 30 mg, 400 mg, and 30 mgwith food. Panel C received 100 mg and 5 mg. In the multiple rising dosestudy, multiple doses of EFdA oral capsules were administered to threepanels of 8 healthy adult subjects. Within each panel, subjects wereadministered three once weekly doses of EFdA (n=6) or matching placebo(n=2) on Days 1, 8, and 15. Panel A received 10 mg. Panel B received 30mg, and Panel C received 100 mg.

In the single dose study, EFdA-TP reached intracellular C_(max) at amedian T_(max) of 6-24 hours and the concentrations in PBMCs declinedwith an apparent terminal half-life of ˜120-210 hours. IntracellularEFdA pharmacokinetics were largely unaffected by a high-fat meal. EFdAwas rapidly absorbed with a median Tmax of 0.5 hour. Plasmaconcentrations decreased in a bi-phasic manner with a rapid initialphase (C_(max) reduced by approximately 10-fold within the first 6-12hours) and a slow terminal phase with an apparent terminal half-life of˜50-60 hours. EFdA plasma exposure appeared to increase in anapproximately dose-proportional manner between 5 and 400 mg.

Intracellular EFdA-triphosphate (TP) pharmacokinetics from the multipledose study are shown in FIG. 2 and Table 1. Plasma EFdA pharmacokineticsfrom the multiple dose study are shown in FIG. 3 and Table 2. Resultsfrom the multiple dose study recapitulate results from the single dosestudy.

Following multiple doses of 30 mg and 100 mg there appeared to be amodest degree of accumulation of EFdA-TP AUC_(0-168 hr) and Cmax, whilethere was little to no accumulation of EFdA-TP C_(168 hr). There waslittle to no accumulation of EFdA in plasma, as anticipated from therelatively short half-life. All subjects had plasma concentrations belowLLQ (3.41 nM) at 48 hr post-dose and later on week 1, and at 96 hrpost-dose or later in week 3 at the 10 mg dose. The exposure of EFdA inplasma and EFdA-TP in PBMC appeared to increase in a generallydose-proportional manner.

TABLE 1 Summary Intracellular EFdA-TP in PBMCs Pharmacokinetic ParameterValues Following Administration of Once Weekly Oral Doses of EFdA for 3Weeks to Healthy Fasted Subjects Geometric Mean (% GCV) AUC_(0-168 hr)Dose (hr * pmol/10⁶ Cmax C_(168 hr) Tmax^(†) t_(1/2) (mg) N Week cells)(pmol/10⁶ cells) (pmol/10⁶ cells) (hr) (hr) 10 6 1  341 (21.2) 3.78(15.3) 0.989 (40.4)  48.00 (24.00, — 96.00) 3 —^(‡) —^(‡) —^(‡) —^(‡)—^(‡) 30 6 1 1160 (41.5) 13.2 (51.3) 3.67 (35.8) 9.00 (6.00, — 24.00) 31570 (12.3) 19.6 (13.7) 5.37 (10.7) 15.00 (6.00, 150 24.00) (21.0)AR^(§) 1.36 (0.97, 1.49 (0.87, 1.46 (1.10, — — 2.28) 2.72) 2.49) 100 6 13020 (31.3) 27.9 (21.2) 13.5 (36.9) 18.00 (6.00, — 48.00) 3 4580 (17.6)43.0 (16.7) 14.3 (27.6) 24.00 (12.00, 162 24.00) (14.6) AR^(§) 1.52(1.12, 1.54 (1.35, 1.06 (0.74, — — 2.44) 2.09) 1.48) PBMC: PeripheralBlood Mononuclear Cells ^(†)Median (Min, Max) ^(‡)30% of PBMC samples ofweek 3 were lost during shipping due to mishandling. Therefore, the PKparameter values could not be determined. ^(§)Geometric MeanAccumulation Ratio of Week 3/Week 1(Min, Max)

TABLE 2 Summary EFdA Plasma Pharmacokinetic Parameter Values FollowingAdministration of Once Weekly Oral Doses of EFdA for 3 Weeks to HealthyFasted Subjects Geometric Mean (% GCV) Cmax Tmax^(†) t_(1/2) Dose (mg) NWeek AUC_(0-168 hr) ^(‡) (μM * hr) (nM) (hr) (hr) 10 6 1 — 193 (40.8)1.00 (0.50, 2.00) — 3 —^(&) 241 (48.9) 1.00 (0.50, 1.00) —^(&) AR^(§) —1.25 (0.70, — — 1.66) 30 6 1 — 647 (25.3) 1.00 (0.50, 1.00) — 3 3.97(18.5) 637 (31.0) 1.00 (0.50, 1.00) 74.1 (14.1) AR^(§) — 0.98 (0.73, — —1.44) 100 6 1 — 1470 (65.1)  2.00 (1.00-6.00) — 3 12.0 (14.8) 1850(62.2)  1.00 (1.00-6.00) 87.1 (9.55) AR^(§) — 1.26 (0.26, — — 3.59)^(‡)AUC_(0-168hr) could not be determined for week 1 as plasma sampleswere collected up to 96 hrs for Week 1 ^(†)Median (Min, Max)^(§)Geometric Mean Accumulation Ratio of Week 3/Week 1(Min, Max)^(&)Values could not be determined due to insufficient data in theterminal phase.

EXAMPLE 3

The single dose monotherapy efficacy of EFDA is currently beingevaluated in HIV-1 patients naïve to anti-retroviral treatment. In thisstudy a single 10 mg dose of EFDA was associated with a rapid and robustreduction in VL. At 168 hours post-dose, a mean (95% CI) placeboadjusted VL reduction of 1.67 log 10 (1.47, 1.87) was observed. Mean VLcontinued to decline through Day 10 with a mean reduction of 1.78 log 10(1.59, −1.98) and no evidence of recrudescence. The 10-mg dose wasgenerally well tolerated with a limited number of mild/moderate adverseexperiences reported. EFDA plasma and EFDA-TP PBMC PK were similar topreviously reported data in healthy subjects. A summary of the placebocorrected change from baseline in viral load for a 10 mg dose isprovided in Table 3 below.

TABLE 3 Placebo Corrected Change from Baseline in Viral Load for a 10 mgDose of EFDA Treatment N Min Median Max SD^(†) LS mean^(‡) (95% CI^(§))PBO 20 −0.52 −0.04 0.42 0.25 −0.03 (−0.13, 0.08) Panel A: 6 −1.97 −1.63−1.31 0.24 −1.67 (−1.87, −1.47) EFDA Posterior mean PP^(||) EFDAadjusted −1.64 >99.9% by PBO ^(†)SD = standard deviation; ^(‡)LS = leastsquares. ^(§)CI = confidence interval. #The PBO data were pooled fromhistorical placebo data from recent monotherapy studies in HIV patientsand fitted with a longitudinal data analysis model containing fixedeffects for study and time, and a random effect for subject. The EFdAdata were fitted with a longitudinal data analysis (LDA) modelcontaining fixed effects for treatment, time and treatment by timeinteraction, and a random effect for subject. ^(||)PP = PosteriorProbability of true mean difference in the plasma HIV-1 RNA reductionfrom baseline between EFDA and placebo at least 0.5 log10 copies/mL

What is claimed is:
 1. A method for the prophylaxis of HIV infection ina subject which comprises orally administering to the subject aneffective amount of a compound of structural formula:

or a pharmaceutically acceptable salt thereof, wherein the dosingregimen is once-weekly, bi-weekly, twice monthly or once-monthly.
 2. Themethod of claim 1 wherein the subject is human.
 3. The method of claim 2wherein the dosing regimen is once-weekly.
 4. The method of claim 3wherein the dosage amount is from 1 mg to 50 mg at each administration.5. The method of claim 2 wherein the dosing regimen is bi-weekly ortwice monthly.
 6. The method of claim 5 wherein the dosage amount isfrom 2 mg to 100 mg at each administration.
 7. The method of claim 2wherein the dosing regimen is once-monthly.
 8. The method of claim 7wherein the dosage amount is from 4 mg to 200 mg at each administration.9. A method for the prophylaxis of HIV infection in a subject whichcomprises orally administering to the subject an effective amount of acompound of structural formula:

wherein the dosing regimen is once-weekly, bi-weekly, twice monthly oronce-monthly.
 10. The method of claim 9 wherein the subject is human.11. The method of claim 10 wherein the dosing regimen is once-weekly.12. The method of claim 11 wherein the dosage amount is from 1 mg to 50mg at each administration.
 13. The method of claim 10 wherein the dosingregimen is bi-weekly or twice monthly.
 14. The method of claim 13wherein the dosage amount is from 2 mg to 100 mg at each administration.15. The method of claim 10 wherein the dosing regimen is once-monthly.16. The method of claim 15 wherein the dosage amount is from 4 mg to 200mg at each administration.
 17. The method of claim 1 for the prophylaxisof HIV-1 infection.
 18. The method of claim 2 for the prophylaxis ofHIV-1 infection.
 19. The method of claim 3 for the prophylaxis of HIV-1infection.
 20. The method of claim 4 for the prophylaxis of HIV-1infection.
 21. The method of claim 5 for the prophylaxis of HIV-1infection.
 22. The method of claim 6 for the prophylaxis of HIV-1infection.
 23. The method of claim 7 for the prophylaxis of HIV-1infection.
 24. The method of claim 8 for the prophylaxis of HIV-1infection.
 25. The method of claim 9 for the prophylaxis of HIV-1infection.
 26. The method of claim 10 for the prophylaxis of HIV-1infection.
 27. The method of claim 11 for the prophylaxis of HIV-1infection.
 28. The method of claim 12 for the prophylaxis of HIV-1infection.
 29. The method of claim 13 for the prophylaxis of HIV-1infection.
 30. The method of claim 14 for the prophylaxis of HIV-1infection.
 31. The method of claim 15 for the prophylaxis of HIV-1infection.
 32. The method of claim 16 for the prophylaxis of HIV-1infection.